An elusive problem faces researchers involved in the correlation of brain form (structure) from x-ray computed tomography (CT) images and brain function (metabolism) from nuclear medicine position emission tomography (PET) images. The difficulty concerns the superposition and registration of the tomographic view obtained from these two imaging modalities. Our approach to this problem is based upon a two-stage solution. First, we are developing practical methods for the accurate and reproducible placement of the head within a tomographic scanner's aperture. Second, we are developing simplified algorithms for the scaling and registration of digitized images from different scanners, on a digital display subsystem. The precise orientation of the subject's skull within the scanner's aperture is monitored and recorded through the use of a commercially available position/orientation transduction subsystem. This six-degree-of- freedom measurement subsystem also appears to be useful for monitoring skull position during a scan and providing data which will facilitate the removal of motion artifact. The driving force behind the goal of brain image registration is the need to develop a greater understanding of the processes underlying the generation of PET images. It is hoped that development of techniques for the accurate correlation of CT structural data with PET metabolic information will enhance this understanding.